1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, a semiconductor device, and a semiconductor device manufacturing apparatus, and for example, the present invention relates to a method of forming a pattern of a semiconductor device pattern using a double exposure method.
2. Description of the Prior Art
Memory devices such as a flash memory, a dynamic random access memory (DRAM), and a static random access memory (SRAM), and semiconductor devices such as a logic device are recently required to be highly integrated, and therefore miniaturization of patterns is essential. To integrate a lot of devices in a small area, the individual devices should be formed in small sizes, and therefore the pitch of a pattern which is the sum of a line width and spacing of the pattern should be made small. However, a photolithography process for forming a desired pattern is limited in resolution, and thus there is a limitation in forming a pattern having a fine pitch.
In recent years, technology (pattern forming technology) of forming a fine pattern on a substrate and processing an under layer of the pattern through an etching process using the pattern as a mask is widely applied in IC fabrication of semiconductor industries and is attracting a great attention. Therefore, as one of lithography techniques which have been newly proposed, a double patterning method for forming a photoresist pattern by performing a patterning two or more times is under investigation. According to this double patterning method, it is considered that a pattern can be formed more finely than a pattern formed by one-time patterning, and as an example of the double patterning method, technology of performing an exposure two or more times is under investigation.
FIG. 9 is schematic view illustrating formation of an insulation film as a protection film used in double exposure. A first resist solvent 602a is applied to a substrate (step A), and then the first resist solvent 602a is exposed (step B). Next, the first resist solvent 602a is developed (step C). If a photoresist is used as the resist, a part exposed to a developer is removed, and then a first resist pattern 603a is formed. In addition, a protection film 704 is formed on the first resist pattern 603a (unexposed) to protect the first resist pattern 603a (step D). In general, a resin based resist material changes in properties if it is heated to a high temperature, and thus it is difficult to form a pattern precisely. Therefore, it is preferable that the protection film 704 be formed at a low temperature to prevent deformation of the first resist pattern 603a, for example, in the range from 20° C. to 120° C. If possible, a thin film having a smaller thickness is preferable. For example, a film thickness of 50 Å or smaller is preferable.
Next, a second resist solvent 602b is applied (step E), and the second resist solvent 602b is exposed (step F). Since the protection film 704 is transparent, both the first resist pattern 603a and the second resist solvent 602b are exposed in step F. An exposed part is removed using a developer to form a second resist pattern 603b (step G). Here, although the second resist solvent 602b can be easily removed, the first resist pattern 603a is not removed because the first resist pattern 603a is protected by the protection film 704.
If a mask gap, that is, the gap between lines, is defined as P0, a mask having a relationship of P1=P2=P3=P0/4 can be formed. Therefore, a process surface (not shown) under the resist can be finely patterned.
However, as shown in FIG. 10, since the protection film 704 is thin, a problem can occur in the developing process of step G: that is, a developer can pass through the protection film 704 to remove the first resist pattern 603a as well as the second resist pattern 603b. As a measure for this, a method of increasing the thickness of the protection film 704 is usually selected; however, as shown in FIG. 11, although the first resist pattern 603a is not removed in step G if the thickness of the 704 is increased, pattern dimensions cannot be precisely controlled and can be P2<P1 or P2<P3, thereby making it difficult to form fine patterns evenly.